Aircraft power-unit suspension system

ABSTRACT

A suspension system for an aircraft power unit having a spacer member mounted on the structure of the airframe. Means are provided for mounting the power unit to the spacer member so as to permit the power unit to vibrate predominantly in one predetermined direction and avoid resonance between the power unit and the airframe structure. The mounting means includes an elastic member such as a torsion bar arranged between and connected to the spacer member and the power unit.

United States Patent 1 [11] 3,727,862 Kaufhold et al. 451 A 17 1973AIRCRAFT POWER-UNIT SUSPENSION SYSTEM [56] References Cited [75]Inventors: Norbert Kaufhold, Bremen-Burg; UNITED STATES PATENTS KlausKonig, Lilienthal; Heinrich Keller, Bremen, n of Germany; Jan 2,057,58210/1362 Kerry ..248/5 X G. de Graaf, Zwanenburg, Nether- 'z zgg l eta!"lands; Jan Johan Blanke 1" v Bakker both of Amstelveen PrzmaryExammerTrygve M. Bllx Netherlands; Carolus Plettenburg, Risjsenhout,Netherlands Attorney Spencer & Kaye [73] Assignee: VereinigteFlugtechnische Werke- ABSTRACT Fokker GmbH Bremen Germany A suspensionsystem for an aircraft power unit having [22] Filed: Nov. 30, 1970 aspacer member mounted on the structure of the airframe. Means areprovided for mounting the power [21] Appl' 93737 unit to the spacermember so as to permit the power unit to vibrate predominantly in onepredetermined [30] Foreign A li atio P i it D t direction and avoidresonance between the power unit and the airframe structure. Themounting means in- NOV. 29, 1969 Germany ..P 1960005.6 eludes an elasticmember Such as a torsion bar ranged between and connected to the spacermember [52] US. Cl ..244/5 4, 248/5 and the power unit [51] Int. Cl....B64b l/24 [58] Field of Search ..244/54; 248/5 5 Claims, 6 DrawingFigures PATENTEDAPR 1 11915 3, 727, 862

SHEET 1 BF 3 INVENTORS. NORBERT .KAUFHOLD mus Kome HEINRICH KELLER JAN6. deGRAAF JAN JOHAN BLANKENZEE HANS BAKKER CAROLUS PLETTENBURG '14" BYATTORNEYS.

PATENTEDAPR 1 71975 SHEET 2 UF 3 ,7 I 1 Q I. MM usmmcu KELLER Inventors.9f NORBERT KAUFHOLD KLAUS KONIG JAN 6. deGRAAF HANS BAKKER 11H;CAROLUSPLHTENBUB ATTORN 8 BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates to a suspension system for anaircraft power unit and has means for avoiding resonance between thepower unit and the airframe structure. This suspension system isparticularly intended for power units which are fastened to the aircraftstructure by means of spacers, and preferably for units arranged abovethe wing assembly.

2. Description of the Prior Art Several techniques are known forfastening power units to present-day aircraft: the most common being thearrangement of the power units at the wings and at the tail. In thesetechniques, the power units are fastened to the airframe structure withthe aid of a spacer member which is commonly called a pylon or powerunit stem. Due to the spring stiffness of the spacer and the airframestructure, and due to the masses of the power unit and airframestructure, vibrations may occur between the power unit and the airframestructure, or components thereof. In the most undesirable case, thepower unit and airframe structure for example, the wing vibrate inresonance. It is known that in such a case the developing mechanicalstresses will exceed the permissible strengths of the individualcomponents. Suitable measures must then be employed to attempt to avoidvibrations in the resonance range and, thus, unduly high mechanicalstresses.

Various techniques are known in the aircraft industry to preventresonance phenomena between an airframe structure and a power unit. Inthese known devices as disclosed in, for example, GermanOffenlegungsschriften (laid-open patent applications) Nos. 1,456,139 and1,456,154, and in German Patent No. 901,260 the power units areelastically mounted with respect to the airframe structure. The elementsemployed for this particular purpose are known as vibration dampeningconnectors The elastic force transmission means provided in theabove-mentioned publications is an elastomer which, in a vibratorysense, acts as a spring as well as a damping means. These elements areextraordinarily suited, however, to absorb high frequency vibrationsthat is, vibrations in the sonic range. It is, therefore, most oftentheir purpose to isolate from the airframe structure structuralvibrations and other vibrations originating in the power unit whichcould excite the airframe components into vibrations. Thus, these knowndevices are a means for avoiding resonance by utilizing the elastic anddamping properties of rubber or similar materials.

Such elastomeric spring and damping members are, however, little suitedto transmit vibrations at frequencies below the sonic range, because thefrequencies in the infrasonic range require longer spring paths. Longerspring paths require more space in the design of the springs and, thus,more undesirable weight in the aircraft. Moreover, the temperatures arevery high in the proximity of a power unit, which would seem to precludeadvantageous use of an elastomeric material. Finally, the life time ofrubber or similar materials, with reference to their elasticity andstability, is relatively short.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to eliminate resonance between the power unit and the airframestructure in order to reduce the unduly high mechanical stresses on thestructural components to a permissible limit. This is accomplishedaccording to the present invention by an elastic member which isoperative between the power unit and the spacer and which permitsvibrations of the power unit to be predomi: nantly uni-directional.

It is known that resonance phenomena in a mechanical vibratory systemwhose natural frequencies are determined by masses and springstifinesses can be eliminated by a change in the latter values. Since,however, in the development of aircraft, a change in the masses of thepower unit and airframe structure, and a change in the springstiffnesses of the spacers and, for example, the bending stiffness ofthe wing, can not be made due to existing aerodynamic and constructiverequirements, this type of tuning off resonance can not be used.Therefore, the insertion, according to the present invention, of anelastic member signifies a particular advantage: the masses or weights,respectively, need not be changed, and the existing spring stiffnessesthat is, those of the entire airframe structure remain unchanged. Afurther advantage of the present invention is that the elastic membercan be exchanged, if required, in a very simple manner; that is, thespring stiffness of the spacer is adjustable. If, for example, the

' aircraft is to be equipped with a stronger that is,

heavier power unit, changes would be required in the dimensions of theairframe; that is, in the spring stiffnesses thereof. In order to meetthis requirement, the elastic member need only be removed from the powerunit suspension system according to the present invention and therespective spring element for example, a torsion bar exchanged foranother such element having a different stiffness.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic, fragmentary,perspective view of an aircraft having a power-unit suspension systemaccording to the present invention.

FIG. 2 is a schematic, fragmentary, side elevation view, partly cutaway,showing a wing section having a power-unit mounted thereon by thesuspension system according to the present invention.

FIG. 2a is a fragmentary cross-sectional, side elevational detail viewof a portion of the suspension system according to the presentinvention.

FIG. 2b is a fragmentary front elevation detail view,

partly in cross section, taken generally along the line A-A ofFIG. 2a.

FIG. 20 is a fragmentary side elevation detail view, partly in crosssection taken generally along line BB of FIG. 2d, showing anotherportion of a suspension system according to the present invention.

FIG. 2d is a fragmentary front elevation view of the portion of asuspension system according to the present invention shown in FIG. 2c.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1 ofthe drawings, a conventional power unit 1, such as a nacelled jetengine, is fastened to a wing 2 of an aircraft by means of a spacermember 3. Member 3 is commonly called a pylon or a power unit stem, aswell as a spacer. The shaded area 8 of FIG. 1 indicates the approximateposition of an elastic member 7 (FIG. 2).

Referring now to FIG. 2 of the drawings, the power unit 1 issubstantially suspended from the spacer member 3 at two points marked byaxis lines and 6, respectively. The spacer member 3 is firmly connectedin a known manner to the structure of, for example, wing 2.

The elastic member 7, which may include a torsion bar, is arranged so asto be substantially parallel to the engine center line 4 of the powerunit 1. The torsion bar 7a is attached to the spacer member 3 by a fork9 and is attached to the power unit 1 by means of an arm which isarranged in the center of the torsion bar.

Axis 5 of FIG. 2 of the drawings schematically designates the positionat which power unit 1 is mounted to spacer member 3.

FIGS. 2a and 2b show details of the rear mounting 6 for mounting engine1 to spacer member 3 by means of elastic member 7. In particular, FIGS.and 2b show the manner in which torsion bar 70 is fastened to engine land spacer member 3. FIG. 2a is a fragmentary cross-sectional sideelevation detail view taken in a vertical plane passing generallythrough elastic member 7 and engine center line 4 (not shown in FIG.2a). FIG. 2b is a fragmentary front elevation detail view, partly incross section taken generally through elastic member 7 along line AA ofFIG. 2a. Torsion bar 7a is splined at both of its ends 9a, 9b. In thismanner, a fast connection between torsion bar 7a and fork 9 isaccomplished. Fork member 9 itself may be mounted to spacer 3 by ahollow pivot 9e (FIG. 2a) which is transmitting forces in the X Ydirections. The fork member 9 may also be mounted to spacer 3, as shownin FIG. 2b, by means ofa flange 9fand screws.

Torsion bar 7a is also splined in its middle portion 100, and is in thisway connected with an arm 10. Fork member 9 is provided with twobearings 9c, 9d by which arm 10 is supported. Thus, an angular movementof arm 10 around axis 7b of torsion bar 70 is facilitated and,furthermore, bending stresses on the torsion bar 7a are avoided. Arm 10is connected with engine 1 at three points: the pivot 10d and two rods11a and 11b. Rods 11a and 1 lb are each fastened to arm 10 by levers 10aand 10b, respectively (FIG. 2b). Because of the engine mounting justdescribed having, in particular, an elastic member 7 according to thepresent invention, engine 1 is able to make angular movements which areindicated by lines 6' and 6" in FIG. 2b of the drawings.

As indicated in FIG. 2 of the drawings, line 5 marks the position wherea front mounting of the engine 1 is placed. FIGS. 2c and 2d of thedrawings give, respectively, a detailed cross-sectional and a frontelevational view of this front mounting. As shown in FIG. 2d, engine 1is fastened to spacer 3 by two struts 5a and 5b, and a pedestal 5d.Struts 5a and 5b are pivotally connected at one end with engine 1 in atangential direction, and their other ends are fastened at a commonpoint to pedestal 5d. This common point is a spherical bearing 50carried by the bearing housing of pedestal 5d. Spherical bearing 50itself carries in its bore a bearing bolt 5e which is engaged by twofork shaped ends of struts 5a and 5b (FIG. 2c). By means of thisspherical bearing 5c, engine 1 is able to make three movements that is,three rotations about the three axes X, Y, and Z, through the middlepoint of spherical bearing 5c. On the other hand, forces from engine 1in the Z and the --Y directions are transmitted by spherical bearing 50to spacer 3. Pedestal 5d is mounted to spacer 3 by means of a pivot (notshown), a flange and screws. The arrangement of the power unit 1 on wing2 represents a mechanical vibratory system which includes the masses ofthe power unit 1 and the wing 2, and the spring stiffnesses of spacermember 3 and wing 2. If, for example, the tip of wing 2 is excited intobending vibrations by a gust of wind, these movements are transmittedthrough spacer member 3, which must be considered as a spring withoutmass in the equivalent mechanical system, to the power unit 1. This unit1 then vibrates predominantly in the y,-y direction. With the insertion,according to the present invention, of an elastic member 7 between thepower unit 1 and the spacer member 3, the resulting spring stiffness ofthe spacer member is reduced; that is, the entire vibratory systembecomes softer. Since the power unit 1 is rotatably mounted at its frontsuspension 5, the elastic member 7 according to the present inventionpermits pendulum movements of the power unit 1 about axis 7b.

The power unit 1 shall move predominantly in the above mentioneddirection, because in this direction the highest stresses on thestructural components of engine and airframe occur.

In this manner, the entire vibratory system is tuned off resonance bythe intermediary of an additional spring stiffness. No resonance occursbetween power unit 1 and wing assembly 2, and unduly high mechanicalstresses on the structural components are avoided.

The design of the elastic member according to the present invention as atorision bar offers the following advantages, particularly when comparedwith elastomers: the elastic member is not particularly sensitive tothermal stresses; and the torsion bar does not require much space and,thus, meets strict space limitation requirements resulting from theaerodynamic design of the spacers.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

I claim:

1. A suspension system for an aircraft power unit, comprising, incombination:

a. a spacer member mounted to the structure of an airframe; and

b. means including a torsion bar for mounting an aircraft power unit tosaid spacer member, said torsion bar having an axis which issubstantially parallel to the aircraft longitudinal axis and external tothe power unit, and being rigidly connected at one point along itslength to said spacer member and at a different point along its lengthto the power unit member.

4. A suspension system as defined in claim 3 wherein said mounting meansincludes a forward and aft mounting; and wherein said aft mountingincludes a fork engaging said spacer member, said torsion bar beingmounted in said fork, and an arm connecting said power unit to saidtorsion bar.

5. A suspension system as defined in claim 4, wherein said forwardmounting includes means for rotatably mounting said power unit to saidspacer member.

1. A suspension system for an aircraft power unit, comprising, incombination: a. a spacer member mounted to the structure of an airframe;and b. means including a torsion bar for mounting an aircraft power unitto said spacer member, said torsion bar having an axis which issubstantially parallel to the aircraft longitudinal axis and external tothe power unit, and being rigidly connected at one point along itslength to said spacer member and at a different point along its lengthto the power unit in such a way that the power unit is permitted tovibrate predominantly in one predetermined direction about said torsionbar axis in order to avoid resonance between the power unit and theairframe structure due to airframe structure vibrations.
 2. A suspensionsystem as defined in claim 1, wherein said spacer member is mounted onthe upper side of a wing.
 3. A suspension system as defined in claim 1,wherein said mounting means additionally has means for rotatablymounting the power unit to said spacer member.
 4. A suspension system asdefined in claim 3 wherein said mounting means includes a forward andaft mounting; and wherein said aft mounting includes a fork engagingsaid spacer member, said torsion bar being mounted in said fork, and anarm connecting said power unit to said torsion bar.
 5. A suspensionsystem as defined in claim 4, wherein said forward mounting includesmeans for rotatably mounting said power unit to said spacer member.